They don't have specific number, they just take the first free slot. (0 to 15)
Also for the players neutral/aggressive, etc, it's done in blizzard.j, and you can change it yourself during the game, (basically setting alliances between players, enemy, ally, and so one)
Finally finding about some of the bots that are flooding the users online - bytespider apparently is a huge offender here - ignores robots.txt and comes in from a ton of different IPs
Ghan has said he has fixed this. Monovertex please confirm this fix. This was only a problem with people that had signatures in the upper levels like not the special members but the respected members.